# form_field_validation 3x

    form_field_validation(3x)                     form_field_validation(3x)

## NAME

           form_field_validation - data type validation for fields

## SYNOPSIS

           #include <form.h>
           int set_field_type(FIELD *field, FIELDTYPE *type, ...);
           FIELDTYPE *field_type(const FIELD *field);
           void *field_arg(const FIELD *field);

           FIELDTYPE *TYPE_ALNUM;
           FIELDTYPE *TYPE_ALPHA;
           FIELDTYPE *TYPE_ENUM;
           FIELDTYPE *TYPE_INTEGER;
           FIELDTYPE *TYPE_NUMERIC;
           FIELDTYPE *TYPE_REGEXP;
           FIELDTYPE *TYPE_IPV4;

## DESCRIPTION

           The  function  set_field_type  declares  a data type for a
           given form field.  This is the type checked by  validation
           functions.  The predefined types are as follows:

           TYPE_ALNUM
                Alphanumeric  data.  Requires a third int argument, a
                minimum field width.

           TYPE_ALPHA
                Character data.  Requires a  third  int  argument,  a
                minimum field width.

           TYPE_ENUM
                Accept one of a specified set of strings.  Requires a
                third (char **) argument pointing to a string list; a
                fourth  int flag argument to enable case-sensitivity;
                and a fifth int flag argument  specifying  whether  a
                partial  match  must be a unique one (if this flag is
                off, a prefix matches the first of any  set  of  more
                than  one  list  elements  with  that prefix). Please
                notice that the string list is  not  copied,  only  a
                reference to it is stored in the field. So you should
                avoid using a list that lives in automatic  variables
                on the stack.

           TYPE_INTEGER
                Integer  data,  parsable  to  an  integer by atoi(3).
                Requires a third int argument controlling the  preci-
                sion,  a  fourth  long  argument constraining minimum
                value, and a fifth long constraining  maximum  value.
                If  the  maximum  value  is less than or equal to the
                minimum value, the range is simply ignored. On return
                the field buffer is formatted according to the printf
                format  specification  ".*ld",  where  the   '*'   is
                replaced  by  the precision argument.  For details of
                the precision handling see printf's man-page.

           TYPE_NUMERIC
                Numeric  data  (may  have  a   decimal-point   part).
                Requires  a third int argument controlling the preci-
                sion, a fourth double argument  constraining  minimum
                value, and a fifth double constraining maximum value.
                If your system supports locales,  the  decimal  point
                character  to  be  used  must be the one specified by
                your locale.  If the maximum value is  less  than  or
                equal  to  the  minimum  value,  the  range is simply
                ignored. On return  the  field  buffer  is  formatted
                according  to  the printf format specification ".*f",
                where the '*' is replaced by the precision  argument.
                For  details  of  the precision handling see printf's
                man-page.

           TYPE_REGEXP
                Regular expression data.  Requires a regular  expres-
                sion  (char  *)  third argument; the data is valid if
                the regular expression matches it.   Regular  expres-
                sions  are  in  the  format  of  regcomp and regexec.
                Please notice that the regular expression must  match
                the  whole  field.  If  you have for example an eight
                character wide field, a regular expression "^[0-9]*$"
                always  means  that  you have to fill all eight posi-
                tions with digits. If you want to allow fewer digits,
                you  may  use  for example "^[0-9]* *$" which is good
                for trailing spaces (up to an  empty  field),  or  "^
                *[0-9]*  *$"  which  is good for leading and trailing
                spaces around the digits.

           TYPE_IPV4
                An Internet Protocol Version 4 address. This requires
                no  additional argument. It is checked whether or not
                the buffer has the form a.b.c.d, where  a,b,c  and  d
                are numbers between 0 and 255. Trailing blanks in the
                buffer are ignored. The address itself is  not  vali-
                dated. Please note that this is an ncurses extension.
                This field type may not be available in other  curses
                implementations.

           It  is  possible  to  set  up new programmer-defined field
           types.  See the form_fieldtype(3x) manual page.

## RETURN VALUE

           The functions field_type  and  field_arg  return  NULL  on
           error. The function set_field_type returns one of the fol-
           lowing:

           E_OK The routine succeeded.

           E_SYSTEM_ERROR
                System error occurred (see errno).

## SEE ALSO

           curses(3x), form(3x).

## NOTES

           The header file <form.h> automatically includes the header
           file <curses.h>.

## PORTABILITY

           These  routines  emulate the System V forms library.  They
           were not supported on Version 7 or BSD versions.

## AUTHORS

           Juergen Pfeifer.  Manual  pages  and  adaptation  for  new
           curses by Eric S. Raymond.

                                                  form_field_validation(3x)